This invention relates to a rotary electrical machine, and particularly to a brushless motor, flywheel magneto or generator.
With many types of rotary electrical apparatus such as motors or generators, there must be provided an arrangement for conveying or receiving electrical current between the rotor winding and the affixed contacts in the machine housing to change the polarity. This is generally done by a brush and commutator arrangement. However, the use of brushes and commutators has a number of disadvantages.
First, the brushes are constantly in sliding engagement with the commutators and thus, there is the problem of wear and noise generation. Also the commutator elements must be electrically insulated from each other. In addition, sparks frequently occur between the sliding surfaces and thus, this type of machine requires regular maintenance and inspection.
Therefore, there has been proposed a type of machine which is called a brushless DC machine that employs permanent magnet fields on the rotor and an armature as the stator. Electric current switching is performed by semiconductor devices such as Hall elements instead of commutators and brushes. This provides a machine that does not require servicing, and produces a higher output more efficiently because of the less frictional drag. Also this avoids the noise and sparking of the prior art type of constructions.
Oftentimes, these devices are utilized as motors in office or factory automation and somewhat less frequency as a power drive for mobile objects such as motor-driven vehicles. The reason for the somewhat limited later type of use is that conventional permanent magnets employing ferromagnetic materials have relatively large size and weight. Also, in many applications, the electrical power is provided by a battery and hence, there are relatively low voltages available and this necessitates high current flows.
Finally, because this device does not have sparking, it is usable in environments where conventional electric motors cannot be employed. However, it is necessary to provide a relatively well-sealed and water-tight arrangement.
With the use of higher efficiency permanent magnets made by rare earth metals, the application of these devices to operation with motor vehicles for driving accessories thereof has become more feasible. However, it is still important to maintain a small and compact size and good relative sealing.
As has been noted, the electrical current switching is performed by a semiconductor devices such as Hall elements. Conventionally, this requires the use of magnetic pole position detectors which are comprised of radially magnetized magnets that are fixed to or carried by discs that rotates in synchronism with the rotor. Hall elements are disposed in close proximity to the peripheral edges of the magnets and provide the necessary signals for switching the current flow to the windings.
With this type of arrangement, however, the rotating magnet carrying disc is spaced from the rotor and outwardly from the armature. In addition, the positioning of the magnets is generally radially outwardly from the rotor and at one end of the armature so that the overall size of the machine becomes quite large. This, therefore, offsets some of the advantages of the utilization of this type of machine.
It is, therefore, a principal object of this invention to provide an improved sensor arrangement for a brushless DC machine.
It is a further object of this invention to provide an improved and compact rotary position sensor for such a machine.
This invention is adapted to be embodied in a rotating electrical machine that has an outer housing in which a stator is mounted. The stator is provided with a plurality of armatures consisting of poles and surrounding armature windings. The stator cooperates with a rotor on which a plurality of circumferentially spaced permanent magnets are affixed. A magnet position sensor arrangement is provided for switching the windings of the armature coils. This sensor arrangement includes a disc that is fixed for rotation with the rotor and which carries a plurality of circumferentially spaced permanent magnets. This disc is disposed radially inwardly of the inner periphery of the armature and cooperates with a sensing plate that mounts a plurality of circumferentially spaced Hall elements.